From:
John Twilley <jtwilley@zzzzzzzzzzz>
Date:
Mon, 06 Dec 2004 11:55:22 -0500
Subject:
mortar for limestone blocks
George,
Hydraulic lime mortar has some of the desirable properties of lime and
some of those of portland cement and it avoids some of the negative
aspects of both. Unlike lime alone, its hydraulic property allows it to
take an initial "set" in a short time period. However, it does not
achieve as high of an ultimate strength as mortar based on cement. This
can be good, because it is more accommodating of slight movements, but
its bond strength is also lower. Cement (unless it's a high grade white
portland cement) usually has a lot of free alkali that leads to
efflorescence. (Even the "low alkali" grade can have up to 0.6% in the
U.S.) Hydraulic lime avoids much of this. Cement also tends to have a
small pore size which means it will draw moisture up the joints by
capillary attraction farther. Hydraulic lime will do this less. The
hydraulic lime will also be slightly "self healing" of hairline
fractures due to the excess lime that it contains. I.e. if stressed, it
will gradually re-harden if not further disturbed.
Most of these objectives can also be obtained with the right
combinations of sand, lime and portland cement (masonry mortar) but
hydraulic lime has the advantage of allowing a thin, grout-like mixture
to do this, whereas a mix based on cement could require a lot of sand to
get the same reduction in hardness.
You can't rely on any mortar for adhesion over the long term, in the
sense of a glue.
John
George Graham wrote:
Quoted text begins.Is it standard masonry practice to always use some sort of spacer for the
joints between blocks of stone and then tuck point the mortar in?
Does the hydraulic lime mortar have any more adhesive properties than
regular mortar?
I have just enough masonry knowledge to create dangerous public works.
End of quote.
- Follow-ups
- message 00471: mortar for limestone blocks - Marcus (06 Dec 2004)
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- message 00464: mortar for limestone blocks - George Graham (06 Dec 2004)
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